A thermal imaging system traditionally consists of a detector, or collection of detectors, sensitive to infrared radiation, and an optical system capable of receiving and focusing said radiation onto the detector. For maximum sensitivity, the infrared detector is often cooled, typically to cryogenic temperatures. In order to maintain the detector at these cryogenic temperatures, a vacuum enclosure is required to minimize thermal losses though heat conduction. This vacuum enclosure is termed a “dewar.”
Unfortunately the length of the traditional combination of an optical system and the detector/dewar is much longer than either the length of the optical system or the detector/dewar alone. This excessive length, and attendant weight, is a serious disadvantage in a number of applications, ranging from portable surveillance equipment to missile warning systems.